The demand for more power efficient and lightweight wireless devices, such as cellular telephones, wireless headsets, and other wireless devices, has required engineers to devise new ways of reducing the size, compactness and integration of the devices' components. Significant strides have been made in reducing the size and compactness of circuit components (e.g., resistors, capacitors, transistors) using integrated circuit technology. However, not all components can be easily formed into an integrated circuit. For example, the antenna and battery, both of which are essential components of any mobile wireless device, are not typically formed as part of an integrated circuit. The power needed to power a wireless device's components is simply too large to allow the battery to be formed at a size that could be practically formed in an integrated circuit.
Antennas are also not typically formed as part of an integrated circuit. An antenna's dimensions and proximity to other conductors affects radiation patterns and efficiency, and the larger the antenna is the better. Furthermore, the high-frequency energy that is generated by the antenna can interfere with other electronics. For these reasons an antenna is usually kept as far away as possible from any integrated circuits, and the antenna is not, therefore, typically formed as part of an integrated circuit.
Because the battery and antenna cannot be easily formed in an integrated circuit, they are typically mounted on a printed circuit board (PCB), along with other electrical components of the wireless device. One type of antenna that is commonly used in such applications is the inverted “F” antenna (IFA). FIGS. 1A-C are top, side, and front views of a typical prior art IFA 100, respectively. As shown in the drawings, the IFA 100 comprises an inverted and horizontally disposed F-shaped electrically conductive structure 102, which is configured over a ground plane 104 formed on a PCB. The F-shaped structure 102 includes an inverted-L element having a vertical ground leg 106 and a long horizontal arm 108, and a vertical radio frequency (RF) feed leg 110. The horizontal arm 108 has a length L. It is configured so that it is at a height h above the ground plane 104. A first end of the vertical ground leg 106 is coupled to a first end of the horizontal arm 108, and a second end of the vertical ground leg 106 is coupled to the ground plane 104. The RF feed leg 110 has a first end that is coupled to the horizontal arm 108, and a second end that is coupled to RF circuitry (not shown) on the PCB.
The length L of the horizontal arm 108 and the height h of the horizontal arm 108 above the ground plane 104 determine the bandwidth of the IFA 100. The resonant frequency of the IFA 100 depends on how well the height h of the horizontal arm 108 above the ground plane is controlled. If the height h is not consistently controlled along the entire length L of the arm 108, the resonant frequency of the IFA 100 is shifted from, or tends to drift from, its desired value. A height h that is not well controlled also adversely affects the impedance matching of the antenna to the PCB and, consequently, results in degraded reception and/or transmission capabilities. Accordingly, it is important that the height h of the horizontal arm 108 of the IFA 100 be well controlled over its entire length L.
In addition to controlling the height h of the horizontal arm 108 of an IFA 100, prior art approaches have focused on isolating the antenna, as best as possible, from conductive objects on the PCB. Conductive objects on the PCB, particularly those which extend substantially above the PCB surface can have the deleterious effect of detuning and/or degrading the radiation pattern of the IFA 100. The battery that is used to power the wireless device is also typically mounted on the same PCB as is the antenna. Since the battery is typically housed in a conductive case, prior art approaches strive to maintain ample separation between the battery and the antenna.
An unfortunate consequence of separating the antenna from the battery is that it prevents the design from being scaled down to a more compact size. In some applications, some degree of compacting can be achieved by “meandering” the length L of the horizontal arm 108 of the IFA 100, or by using a “planar” arm IFA (i.e., PIFA) that has the same or similar effect as an elongated linear arm. However, these approaches are not available if there is no space available on the PCB to accommodate the meandering or planar arm. Even in applications where space is available, the degree to which the design can be compacted is limited by the perceived need to maintain a generous degree of separation between the antenna and battery.
It would be desirable, therefore, to have methods and apparatus which allow an antenna, battery and/or other components of a wireless device to be combined in a manner that allows an overall reduction in size of the wireless device.